The professor of computer science and engineering at Penn State is conducting research that focuses on quantum computation and theoretical computer science. He just received an award from the Department of Defense (DoD) to work on quantum algorithms and one aspect of this is determining which encryption cannot be broken by quantum computers.

Hallgren is one of 11 distinguished faculty to be named to the 2018 Class of Vannevar Bush Faculty Fellows (VBFF) by the DoD. The program provides awards to top-tier engineers and scientists from U.S. universities to conduct “high-risk, high-payoff” research in areas of interest to the DoD over five years, with up to $3 million in support.

“VBFF is oriented toward bold and ambitious ‘blue sky’ research that may lead to extraordinary outcomes such as revolutionizing entire disciplines, creating entirely new fields, or disrupting accepted theories and perspectives,” DoD officials said.

Hallgren will concentrate on the field of quantum algorithms, to determine how to keep cryptography secure. In his abstract, “Exponential Speedups and Limitations of Quantum Computation,” Hallgren said he will be looking at problems that quantum computers can solve but classical computers cannot solve efficiently, specifically in terms of cryptography.

Hallgren hopes his work will help the DoD understand what quantum computers are capable of, as well as work on encryption security in the future.

“Currently used systems can be broken using large scale quantum computers. So far only small quantum computers are available, and cryptography must be replaced before large systems are built,” Hallgren said. “Some of the main proposals for new cryptosystems are lattice-based systems. It is unknown if a quantum computer can solve lattice problems, but if they can, then these systems would also be insecure. This goal of this research is about determining whether or not quantum computers can solve lattice problems.”

Hallgren explained while this is a critically important question, it would not be funded by a regular research grant because the problem is too hard.

“For one thing, if you spend time trying to find a quantum algorithm for these problems, but one does not exist, then you probably end up with no research results,” he said. “Second, even if there is an algorithm, there are no obvious measurable steps to take toward finding it. All the straightforward approaches have been tried. But the upside is that if we are successful in finding quantum algorithms for lattice problems, it will be a major breakthrough in our understanding of what quantum computers can solve, and it will also have a large impact on cryptography.”

Hallgren said it could take multiple years with very little to show, even if the final result is a major breakthrough. Part of the challenge with this area is its interdisciplinary nature. It requires expertise in quantum computation, number theory, theoretical computer science, and cryptography. The DoD fellowship gives him the unique opportunity to carry out this research: It has a longer time frame of five years, and also does not have milestones like a normal grant. It also provides a funding level to put all the pieces in place.